Method of producing finned tubing



Dec. 22, 1970 I |o\ I I E. P. HABDAS METHOD OF PRODUCING FINNED TUBING Original Filed Dec. 13, 1965 n' I L TI: U 31 'l 'I n 30 BMWH 34 i9 IT 59. [H In Ul IU V :fli 2i :fl: V}

26 INVENTOR.

EDWARD F3. HABDAS BY 44 0 20 flan/1 00% 26 ATTORNEY United States Patent 3,548,488 METHOD OF PRODUCING FINNED TUBING Edward P. Habdas, Dearborn, Mich., assignor, by mesne assignments, to Universal Oil Products Company, Des Plaines, 11]., a corporation of Delaware Original application Dec. 13, 1965, Ser. No. 513,248, now Patent No. 3,455,379, dated July 15, 1969. Divided and this application Apr. 3, 1968, Ser. No. 718,619 Int. Cl. B23k 31/02 US. Cl. 29-4773 Claims ABSTRACT OF THE DISCLOSURE Tubing is produced by a method which comprises slitting strip material laterally from one edge to define separated fin forming portions, winding the unslitted portion into helical configuration to form a tube with the fin forming portions extending laterally therefrom. The strip before winding is formed into channel form and the sides of the channel in adjacent convolutions are abutted and bonded together.

CROSS-REFERENCE TO RELATED APPLICATION The present application is a division of my prior copending application Ser. No. 513,248, filed Dec. 13, 1965, now Pat. No. 3,455,379.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to the manufacture of finned tubing from flat strip material. Tubing has been produced from strip material by forming the strip into tubular form and bonding abutting edges of the strip together. This of course does not produce finned tubing. Finned tubing has in general been produced by rolling up the material of a completed tube to provide an integral helical fin, or in some cases, by applying fin material to tubing as a separate construction.

DESCRIPTION OF THE PRIOR ART In my prior Pat. 3,280,841, assigned to assignee hereof, there is disclosed finned tubing produced from strip material by forming the edges of a continuous strip into laterally extending flanges to produce a channel-shaped material. The side flanges of the channel, or at least one of the side channels, is then rolled longitudinally into tapered configuration, thus imparting curvature to the channel construction, after which the channel construction is wound into a tight helical assembly with outer surfaces of the flanges of adjacent convolutions bonded together. The tapering of the flanges is required to avoid tearing of the outer edges of the side walls or other deformation due to the different lengths of material at different radii.

Gortner Reissue Pat. 19,502 discloses fin forming material applied to a prime tube and fails to suggest the production of tubing from the same material which forms the fins.

SUMMARY OF THE INVENTION In accordance with the present invention, continuous flat strip material is slotted laterally from one edge to a point spaced from the other edge by an amount sufl'icient to leave material capable of forming the required tubing and also a short flange for attachment to a flange at the opposite side of the strip. This strip is then wound into tubular configuration, in which the tubing is characterized by having two or more flat sides from each of which extend a mutliplicity of flat fins composed of the Patented Dec. 22, 1970 "ice material between adjacent slits. Inasmuch as the fins extend from flat sides of the tubing, the fins may remain of uniform thickness without producing distortion or requiring treatment to compensate for different radial disstances of portions thereof from the axis of the tubing.

It is an object of the present invention to produce a tube of the character described in the preceding paragraph from strip material by appropriately slitting the strip material, thereafter bending it into channel form, then winding it into a generally helical configuration to produce a transversely elongated tube having flat sides intermediate the rounded ends thereof, and bonding together the generally radially extending flanges to form a closed tube.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing, illustrating preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary view of a strip material cut to prepare it for subsequent tube forming operations.

FIG. 2 is an end view showing the strip material of FIG. 1 bent into generally U-shaped cross-sectional configuration.

FIG. 3 is a fragmentary elevational view showing the elongated folded strip material of FIG. 2 coiled into a closed generally helical configuration to form a finned tube.

FIG. 4 is a fragmentary section on the line 44, FIG. 3.

FIG. 5 is a view similar to FIG. 1 illustrating a different pattern of cuts to produce fins having a double thickness of material.

FIG. 6 is a view of the strip material shown in FIG. 5 bent into U-shaped cross-sectional configuration.

FIG. 7 is a sectional view similar to FIG. 4 showing a different cross-sectional configuration of tube and mandrel.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1-4, elongated strip material 10 preferably of material, is transversely cut to provide slits 11 extending from one edge 12 to a point adjacent to but spaced somewhat from the opposite edge 13. At the inner edge of the slits 11 the strip material is provided with short cuts to provide through slots 14. If desired, the strip material may also be scored along the dotted lines 16 and 18 for subsequent bending altough the bending may be accomplished without scoring the strip.

Referring now to FIG. 2 the strip of FIG. 1 is bent along the lines 16 and 18 into the generally U-shaped configuration shown. The material intermediate the dotted line 18 and the edge 13 forms the narrow continuous upstanding flange 20, the material intermediate the dotted line 16 and the slots 14 forms similar narrow longitudinally spaced flange portions 22, and the material intermediate adjacent slits 11 forms a series of upstanding flange portions 23 which in the folded strip have adjacent edge portions.

The next step in the production of the integral finned tube is to wind the generally U-shaped strip shown in FIG. 2 into generally helical configuration as seen in FIG. 3 around a mandrel a portion of which is shown at 24. The mandrel 24 has the transversely elongated cross'sectional shaped illustrated in FIG. 4 which it will be observed comprises generally semi-cylindrical edge portions 26 interconnected by flat side portions 28. The U-shaped strip of FIG. 2 is wound tightly without spacing between adjacent convolutions so that the narrow continuous flange portion 20 is in abutment with the 1ongitudinally spaced narrow flange portions 22 and with the inner portion of the fin forming portions 23. Since the flanges and 22 are relatively narrow the U-shaped strip material may be wound tightly around the mandrel without additional treatment. It will be understood that as the strip material is wound around the semi-cylindrical end portions of the mandrel the radially outer edge portions of the narrow flanges 20 and 22 are required to be elongated relative to the base portion of the flanges. However, by keeping the flanges 20 and 22 sufliciently narrow this stretching takes place without difiiculty. As an alternative, the narrow flange portions 20 and 22 may be rolled longitudinally to provide an outward taper.

The spacing of the slits 11 and slots 14 is such that the material of the strip intermediate the ends of adjacent slots lies at the fiat side of the mandrel and hence at the flat side of the tube when the material is wound into a tight configuration. The entire fin-forming portion including corner portions 26 remains in fiat condition while generally U-shaped strip shown in FIG. 2 is coiled into the tubular configuration illustrated in FIG. 4.

The construction is completed by providing a suitable bond between the continuous narrow flange 20 and the short narrow flange portions 22 and the inner portions of the flat fin forming portions 23. This bonding is accomplished by welding, soldering, brazing, or the like depending upon the nature of the material from which the tube is formed.

By employing the spaced relatively large fin forming areas in conjunction with the relatively narrow flanges for bonding together and sealing adjacent convolutions of the tube, the effective heat transfer area dependent on the fin area may be substantially as large as desired, while the flange portions employed in bonding adjacent convolutions together may be sufficiently narrow so that the U-shaped strip material may be bent into the required cross-sectional configuration without special treatment of the narrow flange portions.

Referring now to FIG. 5 there is illustrated a somewhat different embodiment in which the strip is relatively wider and is provided with cuts forming slits 31 extending into the strip from opposite side edge portions. Each of the slits 31 extends into one of a series of longitudinally spaced slots 33. The strip material if desired may be scored along bend lines indicated at 34 and 35. In any case, the strip is next bent into the U-shaped configuration shown in FIG. 6 in which the material intermediate the bend lines 34 and 35 and the slots 33 produce short upstanding flange portions 36 and 38 on both sides of the U-shaped strip. As before, these short flange portions are bent around the generally semi-cylindrical edge portions of the mandrel 24. Since the relatively large fin forming areas 40 are provided at both sides of the U-shaped strip of FIG. 6, it will be understood that in the completed finned tube each fin forming area 40 is positioned flat against an adjacent fin forming portion 40, or in other words, the relatively large areas of the tube are of double thickness.

The generally oval or transversely elongated tube configuration is well suited to certain air-cooling applications where minimum pressure drop is desired. This is due to the fact that the thin transversely elongated tube presents a better aerodynamic shape than several round tubes of equivalent surface area.

Referring now to FIG. 7 there is illustrated another embodiment of the present invention in which the slotted tube, folded into generally U-shaped or channel configuration, is wound around a mandrel 42 of generally triangular shape having flat sides 44 interconnected by rounded corners 46. In this case the bottom walls of the channel configuration define a continuous sealed tube 48 of generally triangular configuration and relatively large fiat fins 50 extend outwardly from the tube 48 and specifically, from the flat sides 52 thereof formed by the flat sides 44 of the mandrel 42.

The drawing and the foregoing specification constitute a description of the improved method of producing finned tubing in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. The method of making unitary finned tube from flat strip material which comprises slitting the strip transversely from one edge to a point spaced from the other edge at points spaced along the strip to delineate fins, providing longitudinal cuts at the inner ends of said slits of length to extend around a cylindrically curved side portion of the tube, folding the strip longitudinally into channel shape, thereafter coiling the strip substantially helically into a tubular configuration of abutting convolutions characterized by flat sides corresponding to the dimension between ends of adjacent longitudinal cuts, and bonding the abutting portions of the side walls of the channel shape together to form a sealed tube.

2. The method defined in claim 1 which comprises coiling the channel-shaped strip around a mandrel shaped to conform to the desired tube cross-section.

3. The method defined in claim 1 which comprises slitting the strip from one side and folding the strip longitudinally adjacent the other edge to provide a continuous narrow flange at one side of the channel configuration.

4. The method defined in claim 1 which comprises slitting the strip from both sides, and folding the strip so that flat fins are provided opposite each other at opposite sides of the channel.

5. The method defined in claim 4 in which the fins of adjacent convolutions abut, and bonding abutting fins together.

References Cited UNITED STATES PATENTS 2,372,795 4/1945 Rodeck 113-ll8 2,460,024 1/1949 Mckee l13118 X 3,072,770 1/1963 Goodridge 29477.7 X 3,240,177 3/1966 Habdas 29--157.3 3,255,516 6/1966 Sommer 29--15 7.3 3,362,058 1/1968 Morris et al. 113-118 X JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R. 

